Contemporary computer non-volatile random access mass data storage is often provided by either magnetic disks, such as floppy or hard disks, or optical disks. The magnetic media are accessed with magnetic read/write heads while the optical disks are written and read by lasers. Either type of device is best positioned at the desired location on the disk with a voice coil motor that derives its motive force from a current carrying coil moving in a magnetic field. The magnetic field usually is generated by permanent magnets.
Although the present invention is applicable to any type of magnetic motor, its benefits are especially welcome in the VCM technology where design constraints are particularly stringent. Voice coil motors use permanent magnets to generate magnetic flux, through armatures, to a gap. A coil of wire in the gap is moved by the flux when current is conducted through the coil. The force on the coil is proportional to the current. The coil is, in turn, mechanically connected to suitable structures to move the read/write heads or laser optics.
The armature shape is very important. Since the permanent magnets and armatures must often move with the heads or optics, they contribute to the moving mass and seriously affect seek time. Thus, a minimum weight permanent magnet and armature are required. This conflicts with other needs, however. For maximum motive force, it is important to have a high and uniform flux density in the gap so as to produce a high force in the coil with reduced power dissipation. Uniform flux is needed to keep the force constant as the coil moves in the gap. And yet, the flux must not be allowed to exceed the level that the armature can contain since flux leakage from the armature could be disastrous to the magnetic storage media which operate in very close proximity to the voice coil motor. Optical systems also store data in frozen magnetic domains on the surface of the disk. Spurious magnetic fields could erratically change or erase data.
VCM designers, then, strive for a careful balance of all of the above factors. The most powerful neodymium magnets are used to produce the strongest flux fields for the lightest weight. Armatures are shaped to have just the cross sectional area needed to carry the flux without leakage, and no larger, so as to achieve the lightest weight. Coils may even be wound from square wire to carry the maximum current at the smallest size and weight. As a consequence, VCM's have been built that seek to the selected data track very fast and, in the case of optical systems, focus optics on the data track very fast. Despite these advances, faster data access is a never ending goal. To make even more efficient VCM devices, this invention discloses an improved magnet and armature design which allows still further improvements in the efficiency of the VCM magnetic circuits.